The present invention relates to a method for production of a cooling plate for iron and steel making furnaces, as e.g. blast furnaces.
Such cooling plates for blast furnaces are also called xe2x80x9cstavesxe2x80x9d. They are arranged on the inside of the furnace armour and have internal coolant ducts, which are connected to the cooling system of the shaft furnace. Their surface facing the interior of the furnace is generally lined with a refractory material.
Most of these xe2x80x9cstavesxe2x80x9d are still made from cast iron. As copper has a far better thermal conductivity than cast iron, however, it would be desirable to use copper xe2x80x9cstavesxe2x80x9d. So far a number of production methods have been proposed for copper xe2x80x9cstavesxe2x80x9d.
Initially an attempt was made to produce copper cooling plates by casting in moulds, the internal coolant ducts being formed by a sand core in the casting mould. However, this method has not proved to be effective in practice, because the cast copper plates often have cavities and porosities, which have an extremely negative effect on the life of the plates, the mould sand is difficult to remove from the cooling ducts, and/or the cooling duct in the copper is not properly formed.
It is already known from GB-A-1571789 how to replace the sand core by a pre-shaped metal pipe coil made from copper or high-grade steel when casting the cooling plates in moulds. The coil is integrally cast into the cooling plate body in the casting mould and forms a spiral coolant duct. This method has also not proved effective in practice. A high heat transmission resistance exists between the cooling plate body made from copper and the integrally cast pipe coil for various reasons, so that relatively poor cooling of the plate results. Furthermore, cavities and porosities in the copper can likewise not be effectively prevented with this method.
A cooling plate made from a forged or rolled copper ingot is known from DE-A-2907511. The coolant ducts are blind holes introduced by mechanical drilling in the rolled copper ingot. With these cooling plates the above-mentioned disadvantages of casting are avoided. In particular, cavities and porosities in the plate are virtually precluded. Unfortunately the production costs of these cooling plates are relatively high, however, because the drilling of the cooling ducts in particular is complicated, time-consuming and expensive.
Consequently a method with which high-quality copper cooling plates can be manufactured more cheaply is required.
According to the invention a preform of the cooling plate is continuously cast by means of a continuous casting mould, wherein inserts in the casting duct of the continuous casting mould produce ducts running in the continuous casting direction in the preform, which form coolant ducts in the finished cooling plate. A long cooling plate ready for use can then be manufactured relatively easily from the continuously cast preform without time-consuming drilling. It should be specially noted in this connection that cavities and porosities can be prevented far more effectively in continuous casting than in casting in moulds. Furthermore, the mechanical strength of a continuously cast cooling plate is far higher than that of one cast in a mould. The heat transmission is optimum, because the continuously cast ducts are formed directly in the cast body. As the cross-section of the continuously cast ducts need not be circular, new advantageous possibilities concerning the design and arrangement of the coolant ducts are opened up. It was also established that the special quality of the surface of a continuously cast cooling plate creates good preconditions for the adhesion of a refractory spraying compound.
During continuous casting prongs in the casting duct of the continuous casting mould can produce grooves running in the casting direction in a surface of the preform. These grooves increase the cooled surface of the finished cooling plate and form anchoring points for a refractory lining. However, such grooves can also be subsequently worked, e.g. cut, into a surface of the continuously cast preform. This procedure is necessary for example, if the grooves are to run at right angles to the continuous casting direction.
If particularly thin cooling plates are to be manufactured, the thickness of the continuously cast preform is advantageously reduced by rolling. The rolling makes the crystalline structure of the copper finer, which has a favourable effect on the mechanical and thermal properties of the finished cooling plate. Although the reduction by rolling increases the production costs of the cooling plate, it may thus be advantageous also to roll continuously cast preforms for thicker cooling plates. In this connection it should be emphasised that the ducts integrally cast into the preform surprisingly do not constitute an important obstacle to the subsequent rolling of the preform. This applies in particular, if the integrally cast ducts have an elongated, e.g. oval cross-section.
A plate is cut out of the continuously cast and if necessary rolled preform by two cuts at right angles to the casting direction, two end faces being formed at right angles to the casting direction, the distance between them corresponding essentially to the required length of the cooling plate. It should be noted that several cooling plates of the same or different length can advantageously be manufactured from one continuously cast preform. The production of particularly long cooling plates is likewise possible without additional cost. The plates cut from the preform have several parallel through ducts, which extend in the casting direction and terminate in the two ends.
The cross-section of the integrally cast ducts advantageously has an elongated shape with its smallest dimension at right angles to the cooling plate. In this way, cooling plates with a smaller plate thickness than those with drilled ducts can be manufactured, with the result that copper is saved. It should likewise be noted that ducts with elongated cross-sections can also be produced more easily in continuous casting. A further advantage is that in the case of ducts with elongated cross-sections larger exchange surfaces on the coolant side can be achieved in the cooling plate. Ducts with elongated (e.g. oval) cross-sections, as already described above, behave far more advantageously during rolling of the preform than ducts with circular cross-sections.
In the next production step connection holes terminating in the through ducts for feed and return pipes are advantageously drilled in the plate at right angles to the back, and the end terminations of the ducts are sealed. Connection pieces, which are led out of the furnace armour when a cooling plate is mounted on the latter, can subsequently be inserted in these connection holes.
Each continuosly cast duct can have its own feed and return connection Several continuously cast ducts can, however, also be connected to each other by transverse holes. These transverse holes are, for example, then arranged and sealed in such a way that a serpentine duct with a feed connection and return connection for each cooling plate results.
The cooling plate can advantageously be bent and centered in such a way that its curvature is adapted to the curvature of the blast furnace armour. This is the case in particular if cooling plates with a large width are used. This is likewise the case for cooling plates used in the blast furnace hearth. Such cooling plates for the hearth must in fact fit as closely as possible to the armour to absorb the pressures acting on the hearth lining.